docs: def descendents(class_):
      """
      Return a list of the class hierarchy below (and including) the given class.
  
      The list is ordered from least- to most-specific.  Can be useful for
      printing the contents of an entire class hierarchy.
      """
      assert isinstance(class_,type)
      q = [class_]
      out = []
      while len(q):
          x = q.pop(0)
          out.insert(0,x)
          for b in x.__subclasses__():
              if b not in q and b not in out:
                  q.append(b)
      return out[::-1]